1. Field of the Invention
The present invention relates to a method and apparatus for pouring metal by a method and apparatus for improving the discharge performance of metal pouring vessels by adjusting vessel tilt.
2. Background Art
Attempts have been made to improve the performance of tilting vessels having a submerged tap hole by minimizing slag entrainment. One such attempt calls for tilting the furnace on its pivot or trunnion and decanting the lighter slag from the steel at the lip of the furnace. This method is disadvantageous since the slag and molten metal corrode the refractory lining along the lip of the furnace. Additionally, it is inefficient and wastes metal because decanting most of the slag without carrying over some molten metal is highly difficult, if not impossible. In U.S. Pat. No. 4,431,169 a boom-mounted, elongated stopper is inserted over the tap hole and lowered to constrict the pour when the amount of liquid metal remaining is low. Subsequently, the boom is slightly raised to allow a slow metal pour without creating vortexes. This method requires expensive control equipment. Moreover, placing the stopper directly over the tap hole presents a great difficulty because the tap hole cannot be seen by the operator. In U.S. Pat. No. 5,203,909 a lance is inserted in the furnace above the surface of the slag and provides a pressurized jet of inert gas which blows the slag away from the tap hole. Correct positioning of the lance of maximum effect is difficult, complicated and expensive. Moreover, the use of large amounts of costly inert gases are required.
Other slag entrainment controls include apparatus of U.S. Pat. No. 4,799,650 a closure having a higher specific gravity than slag but lower than steel has an elongated hexahedral extension which acts as a vortex inhibitor. At a liquid metal level determined by the geometry and density of the device, the hexahedral extension enters and obstructs the tap hole, preventing any further pouring. Problematically, this device is prone to flip sideways, allowing the extension to pass by the tap hole without obstructing the flow. Additionally, not only is a substantial amount of steel retained in the furnace when the closure enters the tap hole, but also the closure is difficult to remove from the tap hole. As taught in U.S. Pat. No. 5,044,610 a device having a tetrahedral shape without the elongated extension is a distinct improvement. This device retracts vortex formation, and increases the amount of metal poured before obstruction of the tap hole. However, some slag may still be entrained.
In U.S. Pat. No. 4,718,644 a slag sensor is mounted on a non-ferromagnetic tap hole nozzle. The sensor detects the flow of slag by measuring eddy currents and magnetic fields in the material flowing through the nozzle. Problematically, the sensor does not detect the first presence of slag in the output stream. The proportion of slag in the output stream must increase to a substantial amount before detection. By this point, a significant amount of slag has already passed through the tap hole. A method disclosed in U.S. Pat. No. 6,074,598 improves the accuracy of detecting the initiation of slag contamination in the metal flowing through a tap hole. The method calls for inhibiting the formation of a vortex over the discharge opening in order to reduce the turbulence of flow directly above the tap hole, and limits the premature entry of slag into the tap hole and allows a slag sensor to more easily identify the steel to slag transition.
Another slag separation control is disclosed in U.S. patent application Ser. No. 08/665,992, where a method is disclosed for improving metal pouring by tilting, side-tapping surface. The method provides an optimum tilt angle for pouring determined by the amount of metal residuum, the furnace geometry, and the history of wear in the furnace. The optimum angle is the angle within the critical tilt range which is capable of supplying liquid metal through the tap hole with minimal vortex formation and minimal slag entrainment for any given amount of metal residuum. The critical tilt range is the range on either side of the tilt angle for any given furnace design wherein the tap hole is lowest with respect to gravity. The method increases slag separation as a function of the metal residuum (the amount of metal remaining in the furnace toward the end of the pour) and physical furnace features.
The present invention overcomes the above-mentioned disadvantages by a method and apparatus for improving metal pouring by further increasing the response of the tilt control while maintaining the slag separation in a metal pouring tilting vessel having a submerged tap hole. In general, a selected set of pouring parameters is determined from a group. The pouring parameters include, but are not limited to, the age of the tap hole, the proximity of the charge to the lip of the vessel, the lining geometry of the vessel, the presence of vortexing, and the liquid head over the tap hole. A condition input is received for each pouring parameter selected and the process permits additional tilt control based on the condition input. The tilt angle of the vessel is adjusted to increase the metal yield, including quality and purity, by maximizing the amount of the liquid bath over the tap hole, and thereby maximizing the throughput of liquid metal through the tap hole and maximizing steel/slag separation. The adjustment also limits uncontrolled discharge from the vessel lip.
Another advantage of the present invention is a method to improve metal yield, quality and purity, of a tilting vessel having a submerged tap hole by determining the proximity of the vessel contents to the vessel lip. In response to this determination, the tilt angle of the tilting vessel is adjusted to increase the metal yield, and thereby maximizing the flow rate of liquid metal through the tap hole and maximizing slag separation. The adjustment also limits uncontrolled discharge from the furnace lip.
An additional advantage of the present invention is a method to improve metal yield of a tilting vessel having a submerged tap hole by determining the age of the tap hole of the tilting vessel. The age of the tap hole can be ascertained by a value stored in computer memory or by means of a mechanical counter. The tilt angle of the tilting vessel is adjusted according to the age of the tap hole to increase the metal yield, and thereby maximizing the flow rate of liquid metal through the tap hole and maximizing slag separation. The adjustment also helps limit uncontrolled slag discharge from the vessel lip.
Yet another advantage of the present invention is a method to improve metal yield of a tilting vessel having a submerged tap hole by determining the tapping trajectory from at least one historical pour. The flight path is a diagram that tracks the tilt angle of the furnace as a function of tapping time. The tilt angle of the tilting vessel is adjusted based on the flight path of at least one historical pour to increase the metal yield, and thereby maximizing the throughput of liquid metal through the tap hole and maximizing slag separation. The adjustment also limits uncontrolled discharge from the furnace lip.
A further advantage of the present invention is a method for determining a final drain angle for a tilting vessel having a submerged tap hole. The method calls for measuring the lining geometry of a tilting vessel. The final drain angle is then determined based on the measured inner geometry. The inner geometry can be measured visually or by a laser recognition device.
Yet a further advantage of the present invention is a method for determining a critical height of vortexing for a tilting vessel having a submerged tap hole. The method first determines the inner geometry of a tilting vessel, the amount of metal discharged into the second vessel, the amount charged to the tilting vessel, and the volume of the vessel contents. Thereafter, the critical height of vortexing is determined based on the volume of the vessel contents (determined from the metal discharged and the amount charged) and the inner geometry of the vessel.
Still another advantage of the present invention is a method for determining the heel weight of a closed tilting vessel having a submerged tap hole and giving the operator the ability to control it. The method first determines the amount of metal discharged into the second vessel, the amount of the vessel charge, the amount of the vessel contents, and the temperature of the vessel contents. Based on the temperature of the vessel contents and the amount of the vessel contents (determined from the metal discharged and the amount charged), the heel weight can be determined and subsequently managed.
Moreover, an added advantage of the present invention is a computer-implemented method for improving metal yield by adjusting the tilt angle of a tilting vessel having a submerged tap hole. In general, a selected set of pouring parameters is generated by user input. The pouring parameters include, but are not limited to, the age of the tap hole, the proximity of the charge to the vessel lip, the lining geometry of the tilting furnace, and the liquid head over the tap hole. A condition input is received for each pouring parameter selected and the process permits additional tilt control based on the condition input. The tilt angle of the furnace is adjusted to increase the metal yield, including quality and purity, by maximizing the amount of the liquid bath over the tap hole, and thereby maximizing the throughput of liquid metal through the tap hole and maximizing slag separation. The adjustment also limits uncontrolled discharge from the furnace lip.
Still yet another advantage of the present invention is a process for improving metal yield without the measurement of a tilt angle. A vessel worker adjusts the tilt angle no matter what the current angle is, based on a pouring parameter, such as, but not limited to the proximity of the vessel contents to the vessel lip, the presence of vortexing or the presence of slag in the tapping stream.